Traditionally, millimeter wave (MMW) radio frequency modules have been assembled with “chip and wire” fabrication techniques, such as shown in FIGS. 1 and 2, where microwave monolithic integrated circuit (MMIC) chips 20 along with interconnecting substrates 22, such as made from alumina or fused silica, are bonded to a coefficient of thermal expansion (CTE) matched housing 24, which is normally formed from copper tungsten (CuW) or other similar CTE matched material. Metal plate capacitors 26 are mounted on the CTE matched housing 24 and have wire bonds 28 extending between the metal plate capacitors 26 and MMIC chips 20. Ribbon bonds 30 can extend between the MMIC chips 20 and any interconnections on the substrate 22. Various electrical interconnects 31 and other components can be printed on the substrates by techniques known to those skilled in the art.
FIG. 1 shows that the coefficient of thermal expansion matched housing 24 can have subminiature coaxial connectors (SMA connectors 32) and/or waveguide interfaces. The MMIC chips 20 and the substrates are typically adhered directly to the CTE matched housing by adhesive or other means. Various waveguide or other channels 34 are formed within the housing.
A drawback of this type of prior art “chip and wire” fabrication technique is its relatively expensive cost because of a high parts count and associated assembly costs. The present assignee has also made improvements by using multilayer, low temperature, co-fired ceramic (LTCC) board techniques, including the use of low transfer tape technology, where MMIC chips are mounted to multilayer LTCC boards. Multilayer board techniques reduce fabrication costs relative to the more traditional “chip and wire” fabrication techniques. There is still room, however, for other processing techniques that are improvements over “chip and wire” techniques besides the use of multilayer, low temperature, co-fired ceramic and low temperature transfer tape board techniques.